As costs of medical care increase, the need for more precise and less traumatic medical procedures has increased as well. These procedures result in fewer effects ancillary to those necessary for the specific treatment. Hospital stays may be lessened. Recovery times may be improved. Vascular catheters are used to treat a variety of maladies formerly treated by drastic surgery. For instance, current high performance catheters are used in the treatment of berry aneurysms in the brain, various vascular accidents (such as strokes and contusions), percutaneous transcatheter angioplasty (PTCA), and the like.
Although various different catheter designs may be used in attaining selected treatment sites, many catheters used for the delivery of therapeutic materials such as drugs and vasooclusive devices are over-the-wire catheters. Other catheters used in the vascular system may be of a design which is flow-directed. A few flow-directed catheters are designed to use a simple distal end which is quite floppy and able to be carried along by the flow of blood through the body. Other flow-directed devices utilize small balloons at their distal end which act as "drag anchors" in pulling that distal end through the vascular path. Flow-directed catheters have the advantage of quickly approaching a site through the vasculature if the site is in a high blood flow region. If the selected site is not in the highest velocity courseway, there is little or no chance that the catheter will reach the desired site.
Over-the-wire catheters are especially useful in treating or diagnosing regions of the body which are difficult to reach because of their location, e.g., at the end of distal and complicated routes through the vasculature. This is so since, unlike catheters typically used in the region of the heart, vascular catheters for remote vasculature do not have sufficient strength, stiffness, and ability to transmit torque to allow movement of the catheter by itself to the selected remote site. Consequently, guidewires are used to provide column strength and torsional strength to the overall catheter/guidewire assembly so that these fine vascular catheters can be tracked over the guidewire and steered through pertinent vessels. See, for instance, the disclosure in U.S. Pat. No. 4,884,579 to Engelson.
In general, the method of using a guidewire with a highly flexible catheter is as follows: a torqueable guidewire having a distal, bent end is guided by alternately rotating and advancing the wire in the vascular pathway to the target site. The distal bend allows the attending physician the choice (with the aid of fluoroscopy) to select a route through bends and "Y's" in the vasculature to the target site. As the guidewire is moved along the selected route, the catheter is typically advanced along the guidewire in increments. It is critical that the catheter be able to track the guidewire along the route in which the guidewire has been placed. That is to say that the catheter must not be so stiff at its distal end (for a selected guidewire) that the catheter pulls the guidewire from its previously selected route. Additionally the guidewire must be flexible enough to be able to follow the chosen route. Furthermore, both the guidewire and the catheter must be of sufficient resilience that they not easily kink when a difficult or tight region of vasculature is encountered. The guidewire must ideally have the ability to transmit torque along its length in a controllable fashion--that is to say that a selected wire rotation at the wire's proximal end produces a corresponding rotation at the distal end--so to allow the physician to steer the guidewire as needed. The need to penetrate farther into the vasculature of extremely soft organs such as the brain and liver provide great demands on the physical description of and material selection for guidewires.
If the wire is too thin along its entire length, it is often difficult to transmit torque in a controlled manner along that wire length. Further, the wire may buckle with axial movement due to low column strength.
One solution to many of these problems has been through appropriate choice of material for the guidewire. One such choice of materials is of alloys containing nickel and titanium and which has been treated in a specific fashion to result in a class generally known as nitinols. Typical of such guidewires are those shown in Bates, U.S. Pat. No. 5,129,890 and to Cook, U.S. Pat. No. 5,213,111. Some improvements to such device is using nickel titanium alloys may be found in U.S. Pat. No. 5,409,015 to Palermo. These alloys are especially suitable for accessing deep into vasculature within soft tissue in that for properly chosen alloys, the guidewires have the ability to undergo major bending without any plastic deformation. Although nitinol guidewires are very suitable for deep access into the vasculature, an offset in performance is typically attained because the alloy itself is quite resilient and stores significant mechanical energy. Said another way: a nitinol guidewire that is flexible enough to enter deep tortuous pathways may be difficult to use: a.) the user may not be able controllably to twist or torque the tip of the guidewire into an appropriate position, and b.) the excessive flexibility doesn't permit tracking of the catheter since the stiffer catheter may pull the guidewire from its preselected route. This usability parameter is one which is typically attributable to the size and material found in the more proximal portions of the guidewire.
Increasing the size of the proximal portion of the guidewire raises the lateral stiffness of the guidewire. Increasing the diameter of a nitinol guidewire to a point where the torqueability is improved sometimes will result in a guidewire having a diameter which is too large for easy physical manipulation.
Another tack taken in improving manipulation and insertability of guidewires has been that of coating the wires with various lubricating materials. An early lubricating material has been high molecular weight silicon-derived oils or near-greases. Other more substantial (and permanent) coverings such as polytetrafluorethylene (TEFLON) and various hydrophilic coatings have also been suggested as coatings for these guidewires. Lubricious coatings on guidewires provide a number of benefits. Proper selection of coatings lowers the resistance to axial movement of the guidewire within the catheter. Similarly, the coatings may be used to lower the resistance of the guidewire within the catheter as it is turned or torqued. Slippery coatings on the guidewire lessen the chance that the catheter will kink as it is moved axially along the guidewire.
U.S. Pat. No. 5,129,890 to Bates, et. al was mentioned in passing above. This patent describes a guidewire having a shaped-memory material. The guidewire's central core has an elongated coil attached distally. A thin polymer sleeve, preferably of polyurethane, is positioned adjacent the core wire. The polymer sleeve provides a base for a hydrophilic polymer coating which is placed on the outer periphery of the underlying polymer sleeve. An alternate embodiment of the guidewire is a one in which the proximal portion of the inner polymer sleeve is not coated with a hydrophilic covering.
Another variation is shown in U.S. Pat. No. 4,884,579 to Engelson. Engelson teaches a guidewire having a distal section which allows greater purchase with the vessel walls through which it is placed; that is to say the distal portion is a higher friction portion of the guidewire than is the portion just proximal of the higher friction section. The somewhat more proximal section is covered with a material which renders that section more lubricious. Suitable coating materials include TEFLON, polyurethane, or materials which form the support for hydrophilic polymers.
U.S. Pat. No. 5,213,111, to Cook, shows a composite guidewire made up of a thin stainless steel wire radially surrounded by a shape-memory alloy, such as a nickel-titanium alloy. The guidewire assembly is said to be coated with a polymer layer and 70%-80% of the distal-most portion of the wire can be coated with a hydrophilic polymer to increase lubricity.
U.S. Pat. No. 5,228,453 to Sepetka, shows a guidewire made up of a flexible, torqueable proximal wire section, a more flexible intermediate section with a flexible polymeric tube covering, and a most flexible distal end section. A helical ribbon coil is wrapped about the intermediate core segment between the wire core and the polymer tube covering to increase radio-opacity and to improve torque transmission while retaining flexibility.
U.S. Pat. No. 5,259,393 to Corso, Jr. et. al, describes a guidewire having controlled radio-capacity at the guidewire's distal tip. A single spring mounted on the guidewire has a tightly coiled region and a second more loosely coiled and less radio-opaque region. The loosely coiled region may be coated with a polymer to avoid roughness due to the presence of the coil.
U.S. Pat. No. 5,333,620 to Moutafis, et. al, describes a guidewire having a metal wire core and a high performance plastic sleeve extruded over that core. A high performance plastic is said to be one which has a flexural modulus of at least 150 ksi and an elongation (at yield) of at least two percent (2%). The preferred high performance plastic is a polysulfone. Other suitable high performance plastics are said to include polyimide, polyetheretherketone (PEEK), polyaryleneketone, polyphenylene sulfide, polyarylene sulfide, polyamideimide, polyetherimide, polyimidesulfone, polyarylsulfone, polyarylethersulfone, and certain polyesters. The coextruded compliant jacket is then said to be completely coated with lubricious material which preferably is hydrophilic. The preferred lubricious materials include complexes of polyurethane and polyvinylpyrrolidone.
U.S. Pat. No. 5,372,144 to Mortier, et. al, describes a guidewire having a sleeve element exterior to a guidewire core. The sleeve element apparently is a polymeric material of high elasticity and low flexural modulus such as polyurethane.
None of these documents show a high torque capability guidewire comprising stainless steel and a composite covering of sprayed polytetrafluoroethylene proximally and a hydrophilic covering distally.